Atherosclerosis, a process in which the walls of the arteries thicken due to the accumulation of plaque in the blood vessels, is the cause of most coronary artery disease that can result in heart attacks, strokes, or inadequate circulation to the extremities. Arterial occlusions caused by plaque accumulation may necessitate major invasive surgery, such as a coronary by-pass procedure. However, less invasive, percutaneous methods may be an alternative in treating atherosclerosis. For example, percutaneous transluminal coronary angioplasty (PTCA) involves advancing a balloon catheter through a body lumen to a target treatment site. In one example, a small incision is made near the femoral artery to insert the catheter, which is then advanced to a plaque area in the coronary artery. The catheter has a deflated balloon near a distal end, and the balloon is positioned across the plaque. Once in position, the balloon is inflated to crack or flatten the plaque, thereby restoring the normal patency of the blood vessel. The balloon is then deflated so that the catheter can be removed, allowing blood flow to resume through the dilated blood vessel.
Another percutaneous catheter treatment method involves drug delivery catheters, which may be used alone or in combination with angioplasty balloons. For example, balloons having micropores may be used to deliver a therapeutic bioactive agent to break-up plaque build-up. One disadvantage of drug delivery catheters that utilize balloons is that the drug, once released from the catheter, requires sufficient time to diffuse into the vessel wall of the treatment site. Otherwise, the drug would be washed downstream by the blood flow. In order to provide sufficient resonance time for diffusion of the drug into the vessel wall, temporary blockage of blood flow upstream from the treatment site may be required. As such, a balloon may be expanded upstream from the treatment site to block blood flow. However, if blood flow is obstructed too long, tissue and organs downstream of the inflated balloon may suffer ischemic damage from lack of oxygenated blood. Ischemia occurs when there is an imbalance between oxygen supply and demand, usually caused by clogged arteries, that leads to insufficient oxygen to tissues such as the heart or brain. The two most common types of ischemia are cardiac and cerebral. Cardiac ischemia includes a continuum of conditions, from silent ischemia to angina to acute myocardial infarction (AMI or “heart attack”). Cerebral ischemia includes transient ischemic attacks (TlAs) and stroke. Consequently, the desired dose to a treatment site may not be achieved in a single procedure because the efficiency of drug diffusion into the vessel wall is not optimized, requiring multiple catheter procedures to adequately treat the target site.
Studies have shown that light activated drugs may be used to treat atherosclerosis. However, ischemia risks may be present with the delivery of light activated drugs. The light activated drug is sensitive to light at a specific intensity or frequency, subsequently targeting cells that have absorbed the drug. However, once released into the blood stream near a target treatment area, the drug requires a certain amount of exposure time to the light for activation, as well as time for the drug to be absorbed into the vessel wall of the treatment site. In order to increase the resonance time to deliver effectively a light activated drug, blood flow needs to be obstructed upstream of the drug delivery area, but this creates the danger of causing ischemia to tissue downstream from the target treatment site.